This invention generally relates to inflation devices used in medical procedures, and more particularly, to automated inflation devices having control systems suitable for controlling the inflation and deflation of catheter balloons used in procedures within a body lumen such as a blood vessel. Such procedures include, for example, vascular procedures such as angioplasty for restoring patency of a blood vessel.
Dilatation balloon catheters have been used in increasing numbers in angioplasty procedures to dilate or enlarge body lumens such as blood vessels (including coronary and peripheral arteries) that have been partially or almost completely blocked by stenosis (a narrowing of the lumen due to injury or disease). In addition to vascular procedures such as dilatation of the coronary and peripheral arteries, angioplasty procedures have been used to treat stenoses in other lumens, such as urethral passages, fallopian tubes, etc. Particularly, the procedure for dilating coronary arteries, referred to as percutaneous transluminal coronary angioplasty (PTCA), has provided an effective and less traumatic treatment technique than coronary by-pass surgery or other surgical treatment methods.
In a typical angioplasty procedure, a guiding catheter is percutaneously introduced into the vascular system of a patient and is directed to a point near the site of the stenosis. Subsequently, a guidewire and a dilatation catheter having an inflatable balloon on the distal end thereof are introduced through the guiding catheter with the guidewire slidably disposed within an inner lumen of the dilatation catheter. The guidewire is advanced out of the distal end of the guiding catheter and is maneuvered into the patient's vasculature containing the stenosis to be dilated, and is then advanced beyond the stenosis. Thereafter, the dilatation catheter is advanced over the guidewire until the dilatation balloon is located across the stenosis.
Once in position across the stenosis, the balloon of the dilatation catheter is filled with radiopaque liquid at relatively high pressures (e.g., generally greater than about 4 atmospheres) and is inflated to a predetermined size, preferably the same as the inner diameter of the artery at that location. The inflated balloon radially compresses the atherosclerotic plaque and/or other deposits comprising the stenosis against the inside of the artery wall to thereby dilate the lumen of the artery and allow blood to flow freely therethrough. In a typical PTCA procedure, the balloon is inflated and deflated several times, with the pressure maintained for several seconds during each inflation, until the desired patency in the blood vessel is obtained. The balloon is then deflated so that the dilatation catheter can be removed and blood flow resumed through the dilated artery.
To inflate or deflate the balloon, the physician typically uses an inflation system such as a syringe connected to the catheter and in fluid communication with the interior of the balloon. The physician uses one hand to grasp the syringe body and the other hand to actuate the plunger to pressurize and to depressurize the inflation fluid. Syringe-type inflation systems of the type described are manufactured and sold by Advanced Cardiovascular Systems, Inc. of Santa Clara, Calif. under the trademark INDEFLATOR.
There are some drawbacks associated with a manual inflation procedure such as the one described. For example, each time the physician wants to adjust or change the location of the balloon in the artery, she must use her hand alternatingly on the proximal end of the catheter for maneuvering the balloon to the desired location, and on the inflation device for pressurizing or depressurizing the balloon. Rather than switching hands between the balloon catheter and the inflation device, it is desirable for the physician to be able to simultaneously control the inflation pressure and the location of the balloon in the artery. This simultaneous control of position and balloon inflation pressure is not possible for a single physician using present manual inflation procedures.
Another drawback of manual inflation systems is that the physician may experience hand fatigue as a result of operating an inflation device for several inflation and deflation cycles, each lasting several seconds, during an angioplasty procedure. Additionally, manual inflation devices are typically bulkier than dilatation balloon catheters, and the presence of such a bulky instrument is preferably to be avoided in the immediate area of an angioplasty procedure.
In recent years, automated inflation devices have become known, including microprocessor controlled units wherein a microprocessor provides control signals to a drive unit which advances or retracts a syringe for the purpose of inflating or deflating a balloon catheter. The drive unit can be made to follow a predetermined pressure output pattern, based on the inflation pressure detected by a pressure transducer in fluid communication with the radiopaque inflation media, and an internal clock. Alternatively, inflation devices have been designed for manual activation, but which are monitored and incorporate a unit that displays inflation pressure and time values for example.
However, these conventional automated devices have limitations. For example, they do not take into account variations in individual catheter volume, nor do they take into consideration individual catheter compliance characteristics. As a consequence, differing inflation characteristics between individual catheters (which in manual inflation systems can be sensed and compensated for somewhat by the physician) can be a result. For example, either slower or faster inflation and deflation of individual catheters is one result. Depending on the attributes of the particular catheter, differing time verses pressure plots may be obtained, even between catheters having the same balloon volume. This is not desirable, as uniformity of performance is important in the equipment used in angioplasty. Particularly in PTCA procedures, where the consequences of a miscalculation on the part of the physician as to the equipment's effect on the coronary vasculature can be life-threatening, dependably uniform performance is essential.
Another problem with prior automated inflation devices is that they may over-control the inflation process, or under-control it. For example, equipment that automatically pressurizes the catheter according to a predetermined pattern does not provide feedback to the physician regarding the treatment. Clinical parameters such as arterial wall compliance and catheter compliance may be masked by the system such that the physician cannot sense them and control the procedure in response to such clinical parameters. Thus, inflation times and pressures may not be accurately controlled by the physician as treatment is taking place. Alternatively, in systems that merely monitor the inflation of the balloon inflation times and rates, these parameters can vary due to individual catheter compliance characteristics. Although the physician can sense these differences in system response, and compensate somewhat for them, it would be desirable to eliminate the differences in system response due to individual catheter characteristics inherent in manual systems, including monitored manual systems.
What has been needed and heretofore unavailable is an automated inflation system that frees the physician from the difficulties of manual inflation, but accounts for individual differences in balloon catheters, both as to fluid volume capacity and as to compliance characteristics. Such a system would be able to compensate for individual differences between catheters, so that catheter inflation and deflation characteristics are kept uniform from catheter to catheter, even though the catheters used with the system may have different individual properties. Nevertheless the automated inflation control system should not take ultimate control of the procedure from the physician. The present invention fulfills this need.